Jurisch, A. (Corresponding author)FZJ*

2005
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Report No.: Juel-4198

Abstract: Neogene sediments of the Göynük and Seyitömer areas in NW Anatolia (Turkey) comprise a highly variable succession of siliciclastics and limestones with local high abundances of organic matter typical of oil shales and coal deposits. They were accumulated in small limnic basins representing excellent geological archives for studying environmental changes. This contribution provides a qualitative and quantitative evaluation of the individual mixtures of different organic matter types by organic-geochemical bulk parameters and molecular pyrolysate compositions. In total, more than 170 rock samples were studied along a 35m section from the Göynük, and a 13m section from the Seyitömer area, respectively. Compositional variations of the sediment input were assigned macro- and micro-petrographically and by measurement of the carbonate content. Kerogens were characterised by elemental analyses of total organic carbon, total sulphur and hydrogen indices. Then, 29 selected rock samples were investigated in detail by temperature programmed open-system pyrolysis-gas chromatography. The two sections investigated show extreme variations of organic carbon, sulphur and hydrocarbons. Organic carbon contens of 1.5-66.6% (Göynük) and 0.6-58.6% (Seyitömer) and hydrogen indices ranging from 63-941 mg HC/g TOC (Göynük) and 14-987 mg HC/g TOC (Seyitömer) point to differences in compositions of organic matter. According to variations of the hydrogen index versus organic carbon content, all sedimentary rocks can easily be differentiated in organic rich shales or limestones, oil shales, humic coals and sapropelic coals. The relative molecular abundances of the individual pyrolytic degradation products from temperature programmed pyrolysis-gas chromatography follows the classification of the relative amounts of sapropelic versus humic organic matter. Indvidual compound classes (aromatic hydrocarbons, n-C$_{6-32}$ alkanes+alkenes and C$_{6-32}$ unidentified resolved compounds normalized to 100%) indicate marked differences of the organic matter composition, especially from ratios of alkanes+alkenes to aromatic compounds. Most characteristic are the differences in the amount of C$_{6-32}$ n-alkanes. The variation of sapropelic versus humic organic matter is also expressed by the variation of the ratio of C$_{6-14}$ n-alkanes to aromatics as well as further individual molecular ratios of the pyrolysates. In total, the investigated sedimentary rock sequences could be differentiated in detail not only in respect to their different organic matter types, but also according to their environmental and preservational conditions.

Keyword(s): sedimentation ; geography ; oil shale deposit ; coal deposit

1. Sedimentäre Systeme (ICG-5)